The Vertical Structure of Spiral Disks

该项目包括一项观测活动，以确定大型螺旋星系盘中的质量分布，从而限制暗物质在这些系统内部区域的重要性。在NSF之前的支持下，首席研究员领导了专用积分场光谱仪（或积分场单元，ifu）的开发，用于绘制星系中恒星和气体的运动。利用这台仪器，他最近完成了磁盘质量调查，获得了多色宽带成像和面向视线的星系盘的积分场旋转和速度色散图。这些数据表明，星系盘的质量光比比预期的要低，这意味着没有大量微弱的、非常低质量的恒星，而且暗物质晕在星系内部区域也具有重要的动态意义。然而，这些结论被沿着视线的圆盘实际厚度的不确定性所削弱。为了纠正这种情况，首席研究员、他的合作者和研究生们将进行进一步的观察，重点关注那些与视线平行的类似星系。具体来说，他们将(1)对20个星系进行光度测量，在战略上选择宽和窄的红外光谱带，这将允许不同年龄的恒星群的分离；(2)利用IFU测量了圆盘边缘的转速和速度色散作为与银河系中心和圆盘中部距离的函数，然后将这些量的变化率与动力学模型进行比较，以约束圆盘和暗晕中的引力质量分布；(3)重新检查磁盘质量调查数据，以确定先前在一个星系中关于恒星运动随人口年龄的系统性变化的建议是否在整个样本中得到证实。该项目的广泛影响包括启动nsf支持的仪器科学项目，研究生培训和指导，将研究成果纳入本科课程开发，以及向广泛受众传播结果的公开演讲。

This project comprises an observational campaign to determine the mass distributions in the disks of large spiral galaxies, and thereby to constrain the importance of dark matter in the inner regions of these systems. The Principal Investigator has, with previous NSF support, led the development of special-purpose integral-field spectrographs (or integral-field units, IFUs) for mapping the motions of stars and gas in galaxies. With this instrumentation, he has recently completed the Diskmass Survey, acquiring multi-color broad-band imaging and integral-field rotation and velocity dispersion maps of galaxy disks oriented face-on to the line of sight. These data suggest that galaxy disks have lower mass-to-light ratios than expected, which implies that there is no large population of faint, very low-mass stars, and that dark-matter halos are dynamically important even in the galaxies' inner regions. However, the conclusions are weakened by uncertainties in the actual thicknesses of the disks along the line of sight. To remedy the situation, the Principal Investigator, his collaborators, and graduate students will conduct further observations, focusing on similar galaxies that are oriented edge-on to the line of sight. Specifically, they will (1) make photometric measurements of 20 galaxies, in strategically chosen wide and narrow infrared spectral bands that will permit the separation of stellar populations of different age; (2) make IFU measurements of the rotation speed and velocity dispersions in edge on disks, as functions of both distance from the galactic center and distance from the disk midplane, and then compare the rates of change of these quantities against dynamical models to constrain the gravitating mass distributions in the disk and the dark halo; and (3) re-examine the Diskmass Survey data to determine if earlier suggestions in one galaxy for systematic variation in stellar motions with age of the population are borne out in the entire sample. The broader impact of this project includes the launching of science programs on NSF-supported instrumentation, graduate student training and mentoring and inclusion of research results in undergraduate course development, and public presentations that disseminate results to a wide audience.